Conventionally, a Ni-base directionally solidified superalloy and a Ni-base single-crystal superalloy have been known as a Ni base superalloy. For example, Rene80 (an alloy consisting essentially of 9.5 percent by weight of Co, 14.0 percent by weight of Cr, 4.0 percent by weight of Mo, 4.0 percent by weight of W, 3.0 percent by weight of Al, 17.0 percent by weight of Co, 0.015 percent by weight of B, 5.0 percent by weight of Ti, 0.03 percent by weight of Zr, and Ni as a balance), and Mar-M247 (an alloy consisting essentially of 10.0 percent by weight of Co, 8.5 percent by weight of Cr, 0.65 percent by weight of Mo, 10.0 percent by weight of W, 5.6 percent by weight of Al, 3.0 percent by weight of Ta, 1.4 percent by weight of Hf, 0.16 percent by weight of C, 0.015 percent by weight of B, 1.0 percent by weight of Ti, 0.04 percent by weight of Zr, and Ni as a balance) have been known as a directionally solidified superalloy. Moreover, TMD-103 (Japanese Patent No. 2,905,473) has been known as a third generation Ni-base directionally solidified superalloy.
These conventional Ni-base directionally solidified superalloys is inferior in strength at high temperatures to a Ni-base single-crystal alloy, but they are good in manufacturing yield due to less occurrences of grain misorientation and less cracking at casting and excellent in a point that complex heat treatment is not required. However, strength of a Ni-base directionally solidified superalloy has been required to be improved for practical use. Moreover, a Ni-base directionally solidified superalloy in strength at a high temperature has been desired because rise of turbine inlet temperature is the most efficient in order to improve efficiency of a gas turbine.
Similarly, a Ni-base single-crystal superalloy with further excellent strength at a high temperature has been also desired, though a Ni-base single-crystal superalloy, which is produced by casting, has superior strength at a high temperature.